1. Field of the Invention
The invention relates to a reading circuit, and more particularly to a reading circuit for obtaining the intensity of a light.
2. Description of the Related Art
With the development of technology, input devices for electronic products have achieved great diversity. In various input devices, touch panels are widely used in the display arrays of liquid crystal displays (LCDs), thus, the capability to input data via the display panel of an LCD. When touch panels are utilized for data input, conventional input devices, such as keyboards and mice, are eliminated, thus, usable space is increased. In various electronic products, such as a personal digital assistant (PDA), a notebook computer (NB), a personal computer (PC), and a mobile phone, touch panels are served main input devices and gradually replace the conventional input device
Because the number of communication and electronic products has increased substantially and because products frequently utilize touch panels as input devices, much research has been devoted to touch panel contact techniques. The response method of the touch panel comprises a photo detection method utilizing a sensor produced by a low temperature poly-si (LTPS) technique. Because the sensitivity of the sensor is lower, a thin film transistor (TFT) is utilized to read the detected result provided by the sensor.
TFTs in different positions, however, have different threshold voltages due to manufacturing procedures. When two sensors detect lights having the same intensity, the TFTs are not able to provide the same reading result due to the different threshold voltages.